This invention relates generally to flight control systems, and more particularly, to methods for providing a pilot of an aircraft in flight with a drift advisory.
An aircraft pilot often experiences a multitude of visual stimuli that compete for the pilot""s attention during flight. Many of these stimuli are within the cockpit environment, most originating on the control panel. The control panel communicates a great amount of information, including numerous indications and warnings, to the pilot and merits a great deal of his attention. Particularly during mission scenarios, it may be necessary for the pilot to concentrate so fully on the internal cockpit environment that he may forego looking outside the aircraft for extended periods of time. When a pilot is thus focused and distracted from regularly looking to the external aircraft surroundings, particularly in the direction of aircraft movement, multiple risks can arise not the least of which is potential collision with other aircraft, buildings, structures or terrain features.
While applicable to any type of aircraft, a hovering aircraft such as a helicopter is particularly susceptible to heightened risks in such situations. A helicopter may experience a slow, virtually imperceptible (from a purely sensory perspective) drift in the horizontal or vertical plane that may go unnoticed by an otherwise preoccupied pilot. The horizontal drift may be along a longitudinal axis (i.e., to the fore or aft), a lateral axis (i.e., to the right or left), or a combination of these. Such drift may be caused by shifting winds or an unbalanced horizontal component (e.g., control settings which are not easily set to true zero such as rotary dial controls). Horizontal drift of a hovering aircraft may occur at a very slow speed, and if left unchecked, may result over time in a substantial displacement of the aircraft from the initial location. The usually slow rate of drift increases the likelihood that an otherwise occupied pilot will not observe the cumulative change in the aircraft""s position, and therefore may not implement corrective action in a timely fashion. While the conditions for horizontal drift are most likely to occur with a hovering helicopter, other aircraft which hover (e.g., vertical takeoff or landing (VTOL) aircraft and dirigibles) are also subject to the dangers of unchecked horizontal drift.
Thus, there is a need to alert a potentially preoccupied pilot of a hovering aircraft that the aircraft has drifted. In particular, it is desirable to alert the pilot only after the aircraft has experienced drift sufficient to warrant concern. An alert given prior to a threshold of reasonable concern would likely come to be considered a xe2x80x9cnuisancexe2x80x9d and be ignored by pilots who may already have too many demands on their attention. Conversely, a late alert (i.e., very tolerant) would not fulfill its mission of keeping the pilot and aircraft safe. An appropriate balance must be struck.
The foregoing and other problems and deficiencies in aircraft control systems and displays are solved and a technical advance is achieved by the present invention for a drift advisory system.
It is an object of this invention to provide an aircraft drift advisory system apparatus and method adapted to measure a perspective angle representational of a direction of a pilot""s line of sight in reference to an aircraft longitudinal axis; a navigation system adapted to measure aircraft altitude and drift vector (velocity and drift direction); and, a data processor coupled with the apparatus and the navigation system, the data processor being adapted to: define a foveal cone comprising a cone swept out by a foveal angle rotated about the line of sight; calculate a risk measure whenever the drift direction is not contained within the foveal cone; and, issue a drift advisory that starts when the risk measure equals an advisory criterion and stops when the drift direction reenters the foveal cone.
It is a further object of the present invention to provide a system wherein the risk measure is a drift distance, the drift distance being calculated by integrating the drift velocity over time.
It is a further object of the present invention to provide a system wherein the navigation system further comprises a global positioning system adapted to provide an aircraft location as projected on the earth surface and the drift vector; the data processor is in communication with a terrain map containing a detailed digital topographic description of an earth surface; and, the risk measure is an approach distance to a nearest object as determined from the aircraft location and the terrain map.
It is a still further object of the present invention to provide a system wherein the perspective angle of the pilot""s line of sight is measured as a rotational orientation of the pilot""s head or alternatively as a rotational orientation of the pilot""s eye-line of sight.
It is a still further object of the present invention to provide a system wherein a data processor is coupled to the navigation system, the data processor being adapted to
calculate a difference between an aircraft drift distance in a spatial dimension and a corresponding threshold distance;
calculate the time interval since the aircraft drift distance was last less than the corresponding threshold distance;
compare said time interval to a criterion time; and
issue a drift advisory when said time interval equals or exceeds said criterion time.
The spatial dimension of the present invention can be lateral, longitudinal, or vertical.
The time interval of the present invention can, in alternative embodiments be set to zero when the pilot uses an aircraft control mechanism to alter the location of said aircraft in the corresponding orthogonal dimension.
The advisory criterion of the present invention can, in alternative embodiments, be implemented as a constant or as a predetermined function of the aircraft altitude.
The drift advisory of the present invention can, in alternative embodiments, be implemented as a visual advisory or an auditory advisory.